A standard for a wireless local area network (WLAN) technology is being developed as an IEEE (Institute of Electrical Engineering and Electronics Engineers) 802.11 standard. IEEE 802.11a and b use an unlicensed band at 2.4. GHz or 5 GHz, and IEEE 802.11b provides a transmission rate of 11 Mbps, and IEEE 802.11a provides a transmission rate of 54 Mbps. IEEE 802.11g provides a transmission rate of 54 Mbps by applying Orthogonal Frequency Division Multiplexing (OFDM) at 2.4 GHz. IEEE 802.11n provides a transmission rate of 300 Mbps with respect to 4 spatial streams by applying Multiple Input Multiple Output-OFDM (MIMO-OFDM) at 2.4 GHz. The IEEE 802.11n supports a channel bandwidth of up to 40 MHz, and, in this case, a transmission rate of 600 Mbps is provided.
Currently, an IEEE 802.11af standard for regulating operations of an unlicensed device in a TV whitespace (TVWS) band is being developed.
As a frequency being allocated for TV broadcasting, a TV White Space band includes a UHF (Ultra High Frequency) band and a VHF (very high frequency) band, and the TV White Space band signifies a frequency band that is authorized to use an unlicensed device under a condition that the usage of the unlicensed device does not impede (or hinder) the communication of a licensed device operating the corresponding frequency band. More specifically, a device that is being operated as an unlicensed device may use an available channel or available frequency band that is not being used by the licensed device in the corresponding frequency band. Herein, licensed devices may include TVs, wireless microphones, and so on, and a licensed device may also be referred to as a licensed user, an incumbent user, or a primary user, and so on.
An unlicensed device that wishes to use a TV WS band is required to provide a protection (or guard) function respective to a licensed device. Therefore, in order to acquire available channel information before initiating transmission of a signal in the TV WS band, the unlicensed device must verify whether or not a licensed device is occupying the corresponding band.
In order to do so, the unlicensed device may verify whether or not a licensed device is occupying the corresponding band by performing spectrum sensing. A spectrum sensing mechanism includes an Energy Detection method (a method determining that a high-priority user is using the corresponding band, when an intensity of a received signal is greater than or equal to a predetermined value), a Feature Detection method (a method determining that a high-priority user is using the corresponding band, when a digital TV Preamble is detected), and so on. When an intensity of a signal received in a specific channel is greater than or equal to a predetermined value, or when digital TV Preamble is detected, the unlicensed device may determine that a licensed device is currently using the specific channel. Additionally, when it is determined that a licensed device is currently using a channel that is immediately neighboring the channel that is currently being used, occasionally, depending upon the level of interference being radiated to the neighboring band, the transmission power of the unlicensed device may be required to be reduced.
However, in the TV WS band, in case the unlicensed device depends only upon frequency sensing in order to acquire the available channel information, more load caused by the sensing process for performing operations may be added to the unlicensed device, thereby causing delay in the procedure. Accordingly, the unlicensed device may acquire available channel list information within a corresponding region, by accessing a geo-location database through the internet or a dedicated network.